Current methods for retrieving silver from manganese (Mn) ores with occluded silver (Ag) do not produce adequate yields. In the best of the cases, current methods reach 30% recovery yield, as when direct cyanidation is used, and those who reach it require complicated and expensive processes where the silver must be found in high concentrations in order to reach an acceptable yield. Currently, little progress or developments exist. The main objective of these processes is to release the occluded silver, either by grinding, which may be unaffordable, or by chemical methods.
Acanthite (Ag2S) is considered to be the main ore source of silver and pyrolusite (MnO2) is considered to be the main ore source of manganese, from their association a manganese-argentiferous ore is produced.
Currently, it can be found, on scientific literature and patent documents, methods for recovering manganese using methods such as roasting and leaching. Zhang and Yong Cheng (Zhang, W., Cheng, Ch Y, 2007, Manganese Metallurgy Review Part I: Leaching of ores/secondary materials and recovery of electrolytic/chemical manganese dioxide. Hydrometallurgy 89:137-159), review of such processes, where the ore to be recovered is MN, in view of its use on batteries.
In the case of the roasting, a pyro-metallurgical pretreatment including melting (Cooper, H. S., Schaefer, J. C., Schmidt, E. C., 1959, Recovery of manganese from metallurgical by-products by chlorination. U.S. Pat. No. 2,877,110; reduction-roasting (Rolf, R. F., 1969 in “Selective recovery of manganese and iron from ores”. U.S. Pat. No. 3,471,285); sulfation (Freitas, L. R., Amaral, J. C., Mendonga, C. F., 1993. Sulfation of carajas manganese ore with gaseous SO2″, Transactions of the Institution of Mining and Metallurgy, Section C—Mineral Processing and Extractive Metallurgy 102, C130-C131); and chlorination, (Cooper, H. S., Schaefer, J. C., Schmidt, E. C., 1959, Recovery of manganese from metallurgical by products by chlorination. U.S. Pat. No. 2,877,110). In all these cases, the final objective is to obtain manganese in a soluble form, mainly as a sulphate.
In regards to leaching, the first process to be carried out may include chemical dissolution, bioleaching, electrolysis, and electrodeposition, among others. In general, the reagent used is acidified ferrous sulphate (Brantley, F. E., Rampacek, C., 1968. Manganese and iron recovery from leach solutions. U.S. Pat. No. 3,397,130); (Das, S. C. Sahoo, P. K. Rao, P. K., 1982. Extraction of manganese from low-grade manganese ores by ferrous sulfate leaching”, Hydrometallurgy 8 (1), 35-47).
Also, there are being reported different methods using sulphur dioxide or sulfite solutions (Petrie, L. M., 1995, Molecular interpretation for SO2 dissolution kinetics of pyrolusite. manganite and hematite, Applied Geochemistry 10 (3), 253-267; (Das, S. C. Sahoo, P. K. Rao, P. K., 1982, Extraction of manganese from low-grade manganese ores by ferrous sulfate leaching. Hydrometallurgy 8 (1), 35-47); (Grimanelis, D., Neousyngouna, p., Vazarlis, H., 1992. Leaching of a rich Greek manganese ore by aqueous-solutions of sulfur-dioxide. Hydrometallurgy 31 (1-2), 139-146); (Ravitz, S. F., Wyman, W. F., Back, A. E., Tame, K. E., 1946. The dithionate process for recovery of manganese from low-grade ores. American Institute of Mining Metallurgical Engineers Metals Technology 13 (No. 6, Tech. Pub. No. 2064) 10 pp); (Naik, P. K., Nathsarma, K. C., Das, S. C., V. N. Misra, 2003, Leaching of low-grade Joda manganese ore with sulfur dioxide in aqueous medium. Transactions of the Institutions of Mining and Metallurgy, Section C: Ore Processing and Extractive Metallurgy 112 (2), C131-C134); (Ward, C. B., 2005. “Acidic leaching of manganese from lean oxide ores with extraction stage for purity. WO Patent No. 2005012582); (Maslenitskii, N. N., Mil'ner, R. S., Belikov, V. V. 1969. Laboratory study of dithionate treatment of three samples of low-grade manganese slimes. Obogashchenie Rud (Sankt-Peterburg, Russian Federation) 14 (2), 45); (Sventsitskii, A. T., Nosenkov, A. N., Trunev, S. V., Dmitrevskii, B. A., Treushchenko, N. N., Yur'eva, V. I., Ivanova, N. Y., 2003. Acidic leaching redox of lean manganese ores, slimes, and dust from ferroalloy furnaces. RU Patent No. 2213155); Partenov, D., Stefanova, V., Avramov, a., Chimbulev, M., 2004. Kinetics of leaching of polymetallic concretions in an aqueous solution of SO2. Izvestiya Vysshikh Uchebnykh Zavedenii, Tsvetnaya Metallurgiya (1), 15-19); (Abbruzzese, C., 1987. Aqueous SO2 processing of manganese ores. In: Davies, G. A. (Ed.), Separation Processes in Hydrometallurgy, Society of Chemical Industry. Ellis Horwood Limited, London, pp. (77-87); (Pahlman, J. E., Khalafalla, S. E., 1988, Leaching of domestic manganese ores with dissolved sulfur dioxide. U.S. Bureau of Mines Report of Investigations, Twin Cities, US); (Abbruzzese, C., 1990, in “Percolation leaching of manganese ore by aqueous sulfur dioxide. Hydrometallurgy 25 (1), 85-97). In all these cases, if there is silver associated, it can be released and later be recovered by cyanidation, and it is then when the Mn becomes a byproduct, of industrial interest, but subordinated to the silver higher commercial value.
With regard to manganese ores with occluded silver, where the treatment is focused on the recovery of silver, there are some reports that include an immersion treatment of manganese-argentiferous ore in sulfuric acid-sulphur dioxide, with the removal of impurities using an oxidation method—neutralization {Li Haiyan, Han, y., Liu, k. 1993. A method to produce manganese sulfate and to extract silver. International patent C22B11/08; C22B3/04, CN1993103953 19930407; CN1031413 (C)}.
Simultaneous leaches of manganese and silver have been proposed by using sulfuric acid combined with hydrogen peroxide with good silver recoveries (Jiang, T., Yang, y., Huang, z., Qiu. G. 2003. Simultaneous leaching of manganese and silver from silver-manganese ores at room temperature. Hydrometallurgy 69:177-186 and Jiang, T., Yang, y., Huang, z., Zhang, B., Qiu, g. 2004. Leaching kinetics of pyrolusite from manganese-silver ores in the presence of hydrogen peroxide. Hydrometallurgy 72:129-138). Also, there have been reported silver recoveries by a combination of sulfuric acid and sodium sulfite (see Tian, Q-h, Jiao, C-y., Guo, X-y. 2012. Extraction of valuable metals from silver-manganese ore. Hydrometallurgy 119-120:8-15).
The present invention presents a new and economically attractive methodology for the recovery of silver from manganese-argentiferous ores, using sulphur dioxide as the leaching agent, with silver recovery greater than 85%, and able to be implemented in a silver recovery plant without major modifications.